Method for reduction of oil, alkalinity and undesirable gases using a mechanical flotation device

ABSTRACT

A mechanical vessel may effectively and simultaneously displace a first undesired gas from within water with a second desired gas, and remove at least one alkaline species and oily matter from the water. The vessel raises the pH of the water and reduces the lime requirement for subsequent lime softening. The vessel receives the water containing the first gas and passes the water through a series of gasification chambers. Each gasification chamber may have a mechanism that ingests and mixes a second gas into the water thereby physically displacing at least a portion of the first gas into a vapor space at the top of each gasification chamber from which it is subsequently removed. There is an absence of communication between the vapor spaces of adjacent chambers. An acid is added to remove the alkaline species, where the first gas is an optional by-product that is also removed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No. 12/197,579filed Aug. 25, 2008, which issued May 8, 2012 as U.S. Pat. No.8,173,016, which in turn is a continuation-in-part application of U.S.Ser. No. 11/096,786 filed Apr. 1, 2005, which issued Aug. 26, 2008 asU.S. Pat. No. 7,416,661, all of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for removing agas from a liquid, and more particularly relates, in one embodiment, tomethods and apparatus for simultaneously separating a gas, oil and analkaline species from water.

In many industries, including oil, paper and pulp, textile, electricitygenerating and food processing, there is an ever-present problem ofhandling water contaminated with various substances. In particular,water is often used to aid in the production of oil and gas on offshoreplatforms as well as on land. This water is usually pumped into aformation in order to be able to pump oil out.

One process where water is used to recover hydrocarbons is SteamAssisted Gravity Drainage (SAGD). This process has been testedextensively in the heavy oil and bitumen reservoirs in Canada and hasbeen generally successful, particularly in the very viscous AthabascaTar deposits.

Athabasca Tar (also called bitumen) occurs mainly in the McMurrayformation of the Lower Cretaceous, which lies unconformably on anerosional surface of Devonian carbonate rock. The matrix is mostlyunconsolidated, very fine to coarse-grained, quartz sand of variablethickness. In places the sand is thick with net pay zones from 20 to 40meters in thickness, 30-40% porosity and contains 10 to 18 wt % ofbitumen. A small fraction of the deposit (<10%) is at a depthsufficiently shallow to allow recovery by open pit mining and this hasbecome a very large industrial activity.

Prior to the demonstration of the SAGD process, several other processesfor the in situ recovery of Athabasca tar were tested. These includedcyclic steam stimulation, in situ combustion, electric heating, andother horizontal well processes. All of these approaches were relativelydisappointing and SAGD is the only process that has shown economicpotential.

The SAGD process involves a long horizontal production well located atthe bottom of a reservoir. Steam is injected into a second horizontalwell placed a few meters above this producing well. For very viscousbitumen it is usual to circulate steam in both wells to heat theintervening reservoir and allow communication. After communication isachieved steam is injected continuously into the upper well andcondensate and heated oil are removed from the lower one. Production isrestricted to allow heated oil and condensate to be produced withoutlive steam. This form of operation is well-established and relativelysimple to control. The production well must be long and horizontal sothat an economic oil rate can be achieved without steam coning.Conventional vertical wells are not practical with SAGD. Rates of theorder of 0.2 to 0.4 or more B/d are achieved per foot length ofhorizontal well (0.1 to 0.2 m³/d per meter of horizontal length). Aproduction well 750 m long (2460 ft) may produce about 1000 B/d ofAthabasca bitumen. After treatment, the produced water is reinjected.

A “Wet Steam Generator” is typically used to produce steam for SAGDoperation. The produced water is normally treated to a quality levelsuitable as feed water to the steam generator. The feed water qualityrequirements are: oil less than 1 ppm; hardness (expressed as CaCO₃)less than 1 ppm, suspended solid less than 1 ppm; and silica less than50 ppm depending on the pressure rating of the steam generator. Hardnessof the produced water can be economically reduced to 1 ppm or less by azeolite softening process if the total dissolved solid (TDS) in theproduced water is less than typically 5,000 ppm. Lime softening will beutilized if the TDS of the produced water is high. “Hot/warm” limesoftening has added benefits, in that it will reduce/remove silicacontent from the produced water.

It is interesting to note that lime will react with Ca(HCO₃)₂ and CO₂.If the produced water contains excessive alkalinity and CO₂, it may bemore economical to reduce/remove them prior to the lime softeningprocess. Ca(HCO₃)₂ will react with H₂(SO₄) and produce water, CO₂ andCaSO₄ which will precipitate. Removing alkalinity and CO₂ from theproduced water will greatly reduce the lime dosage.

If the produced water contains excessive TDS, for instance greater than5,000 ppm or higher and high silica content, e.g. 50 ppm or higher, thena typical process train for produced water treatment will consist of anoil/water separator, a flotation unit, a lime softening clarifier, awalnut filter and a weak acid ion exchanger and steam generator. If TDSis less than 5,000 ppm and silica content less than 50 ppm, then theprocess train will consist of an oil/water separator, a flotation unit,a walnut filter and a zeolite ion exchanger.

Apparatus for ingesting and mixing gas into a liquid body are known,such as that of U.S. Pat. No. 3,993,563, which includes a tank, arotatable impeller fixed to a vertical drive shaft, and avertically-extending conduit which surrounds the drive shaft and whichextends to location in the liquid above the impeller to serve as achannel of communication between a source of gas and the impeller.

U.S. Pat. No. 6,660,067 to Stacy, et al. (Petreco International, Inc.)teaches that a mechanical device may be used to effectively displace afirst undesired gas (e.g. oxygen) from within a liquid with a seconddesired or at least inert gas (e.g. nitrogen). The device is a vesselthat receives the liquid containing the first gas and passes the liquidthrough a series of gasification chambers. Each gasification chamber hasat least one mechanism that ingests and mixes a second gas into theliquid thereby physically displacing at least a portion of the first gasinto a vapor space at the top of each gasification chamber from which itis subsequently removed. There is an absence of communication betweenthe vapor spaces of adjacent chambers. The ingesting and mixingmechanisms may be a dispersed gas flotation mechanism, and may be aconventional depurator. The liquid now containing the second gas andvery little or none of the first gas is removed from the vessel for use.

It would be desirable if a method and apparatus were devised that couldsimultaneously remove oil, gas and alkaline species from contaminatedwater.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anapparatus for simultaneously removing a gas (e.g. CO₂) and at least onealkaline species from a liquid, particularly water.

It is another object of the present invention to provide a mechanical,cylindrical gas scavenger machine for chemical scavenger treatment toreduce gas and alkaline species content in a fluid such as water.

Another object herein is to provide a method and apparatus forsimultaneously removing a gas, an alkaline species and oil from producedwater while raising its pH.

In carrying out these and other objects of the invention, there isprovided, in one non-restrictive form, a gas and alkali species removalapparatus that involves a vessel having an inlet and an outlet. Thevessel also has a plurality of partitions between the inlet and theoutlet sequentially dividing the vessel into at least a firstgasification chamber and a second gasification chamber. Each adjacentchamber fluidly communicates with one another. Each chamber has a vaporspace, but there is an absence of communication between the vapor spacesof adjacent chambers. There is a gas feed present in at least the firstgasification chamber. Each gas feed has a flow control device. There isalso present an acid feed tube in each gasification chamber. Each acidfeed tube has a flow control device. There is also present an alkalifeed tube in at least the last gasification chamber. The lastgasification chamber may be the same as or different from the secondgasification chamber, in the non-limiting case where there are only twogasification chambers. There is also present a first gas and acidingesting and second gas displacing mechanism in each gasificationchamber. There is further present in each chamber a gas outlet, whereeach gas outlet having a flow control device.

There is additionally provided, in another non-limiting embodiment asteam assisted gravity drainage (SAGD) system that includes a horizontalproduction well in a subterranean formation. The horizontal productionwell is connected to a production line adapted to supply steamcondensate and heated hydrocarbons to an oil/water separator. Theoil/water separator has a conduit of produced water connected to a gasand alkaline species removal apparatus, also called a mechanicalflotation device herein. The gas and alkaline species removal apparatusincludes a vessel which contains an inlet and an outlet. The vessel alsohas a plurality of partitions between the inlet and the outlet thatsequentially divides the vessel into at least a first gasificationchamber and a second gasification chamber. Each adjacent chamber fluidlycommunicates with one another. Each chamber has a vapor space, but inthe absence of communication between the vapor spaces of adjacentchambers. A gas feed is present in at least the first gasificationchamber. Each gas feed has a flow control device. Each gasificationchamber also has an acid feed tube. Each acid feed tube has a flowcontrol device. Each gasification chamber has a first gas and acidingesting and second gas displacing mechanism therein. A gas outlet isalso present in each chamber. The gas outlet has a flow control device.A clarified water line extends from the outlet of the gas and alkalinespecies removal apparatus to a lime softening clarifier sequentiallybefore a wet steam generator. The wet steam generator is adapted toinject steam into the subterranean formation through an injection line.

Further there is provided a method for simultaneously removing a firstgas and at least one alkaline species from water, where the methodincludes providing a vessel that has an inlet and an outlet and aplurality of partitions sequentially dividing the vessel into at least afirst gasification chamber and a second gasification chamber. Eachadjacent chamber in the vessel fluidly communicates with one another.Each chamber has a vapor space. There is an absence of communicationbetween the vapor spaces of adjacent chambers. The method furtherinvolves introducing a flow of water that includes a first gas and thealkaline species into the first gasification chamber through the inlet.Additionally the method involves introducing an acid into at least thefirst gasification chamber and introducing a flow of a second gas intoeach of the gasification chambers thereby creating a turbulent area. Theintroducing and turbulence displaces at least a portion of the first gasfrom the water into the vapor space of the respective gasificationchamber with the second gas. The method further includes reacting theacid with at least a portion of the alkaline species. The method finallyinvolves removing the displaced first gas from the vapor space of eachgasification chamber, and removing the clarified water from the vesselthrough an outlet therein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic illustration of the mechanical flotation device ofthe invention integrated into a steam assisted gravity drainage (SAGD)process; and

FIG. 2 is a schematic, cross-sectional illustration of one embodiment ofthe mechanical flotation device of the invention.

It will be appreciated that the Figures are schematic illustrations thatare not to scale or proportion, and, as such, some of the importantparts of the invention may be exaggerated for illustration.

DETAILED DESCRIPTION OF THE INVENTION

The method and apparatus herein address the oil removal and alkalinityreduction of water produced in an industrial operation, such as ahydrocarbon recovery operation utilizing a SAGD technique, includingremoving a gas dissolved or mixed in the water. However, the apparatusand method is not limited to the SAGD method and system. In onenon-limiting embodiment, the reduction of alkalinity is achieved byadding typically H₂SO₄ to react with an alkaline species and produce CO₂and water. A scrubbing gas will remove CO₂ from the produced water andhence increase the pH of the produced water. This will result in thereduction of lime usage in a subsequent lime softening process in twoways: (1) not as much lime is required to react with the alkalinity and(2) for effective lime softening, pH of the water will be in the rangeof about 9.0 to about 10.3 alternatively in the range of about 9.5 to10.2; i.e. since the reduction of CO₂ will raise the pH of the producedwater, the lime requirement is therefore reduced.

Main goals of the apparatus and method include, but are not necessarilylimited to (a) the addition of acid to convert alkalinity to CO₂ andwater, by injecting and mixing acid in the each cell (primarily thefirst cell); (b) introduction of scrubbing gas to strip CO₂ from theproduction water; (c) the raising of pH due to the removal of CO₂ fromthe produced water in that it will reduce the lime requirement for limesoftening downstream; and (d) the removal of oil from the produce water.All these four functions can be achieved by the inventionsimultaneously.

In another embodiment of the apparatus and method herein, sometimesproduced water which contains excessive alkalinity requires or benefitsfrom the addition of caustic or other alkaline materials to raise the pHof the water. Certain processes that may be used to treat producedwater, in non-limiting examples, reverse osmosis (RO) or nano-membraneprocesses, may perform better in a high pH environment. Also, in manySAGD processes, the feed water to the steam generator will require waterwith a pH higher than 9.

The present method and apparatus will be further described, by way ofexample, and not limitation, with the influent or treated liquid beingwater that contains a first gas, at least one alkaline species, andoptionally oil, that is treated to at least partially remove the firstgas, the alkaline species and the oil, if present. However, it will beappreciated that the methods and apparatus herein are not limited tothis particular liquid or to these particular gases or to the particularalkaline species discussed. It is expected that the methods andapparatus will find utility with liquids other than water and gasesother than carbon dioxide (CO₂) and alkaline species other than calciumbicarbonate (Ca(HCO₃)₂). It is to be understood that the presentinvention has utility in numerous applications in which it is desirableto replace one gas from a liquid with another, and that the replacedgas, the liquid containing the new gas, or both may be the desiredproduct of the process. Further, the skimmed oil from the liquid or theclarified liquid itself or both may be desired products.

Shown in FIG. 1 is a schematic illustration of one embodiment of themechanical flotation device or gas and alkaline species removalapparatus 10 herein integrated into a steam assisted gravity drainage(SAGD) process that obtains steam condensate and heated hydrocarbons 100(oil, bitumen, and the like) from first horizontal production well 102in the lower part of subterranean formation 104 as steam 106 is injectedinto second horizontal well 108 positioned above production well 102.Produced steam condensate and heated hydrocarbons 100 are removedthrough production line 110 and separated in oil/water separator 112into hydrocarbon portion 114 and conduit of produced water portion 14which is sent to mechanical flotation unit 10.

Produced water 14 containing a first gas (e.g. CO₂), at least onealkaline species, and likely hydrocarbon contaminants (e.g. oil,bitumen, and the like) is treated in flotation apparatus 10 with secondgas 66 and acid 68, and optionally alkali (introduced by alkali feedtube 86), to give clarified water 70, skimmed hydrocarbons 72 andremoved first gas 74 (e.g. CO₂). Clarified water 70 is treated in a limesoftening clarifier 116, walnut filter 117 and unit 118, which may be azeolite or weak acid ion exchanger or the like, before being heated intosteam 106 by wet steam generator 119 and injected into formation 104through injection line 120.

Referring now to the FIG. 2, the flotation unit 10 of the apparatus ofone non-restrictive embodiment herein includes a vessel 12 for receivinga flow of liquid 14 having a first gas, at least one alkaline speciesand optionally oil or other hydrocarbon mixed therewith, where thevessel 12 in one embodiment has a continuous cylindrical sidewall and iscapable of withstanding substantial internal pressures. Vessel 12 isdivided into a feed box or inlet chamber 16, at least a firstgasification chamber 18, a second gasification chamber 20, and an outletor discharge chamber 22, where each adjacent chamber can fluidlycommunicate with one another, that is, that a fluid in one chamber mayand should flow into an adjacent chamber in a sequential or orderedmanner.

The outlet chamber 22 may optionally function in secondary first gaschemical scavenging. Outlet chamber 22 may optionally provide aninjection booster pump plus level control as typically used in theprocess, though these latter functions will not influence the removal ofthe first gas by the second gas. It should be apparent that the flow ofthe liquid is from the inlet 30 to the outlet 34. The particular vessel12 shown in FIG. 2 also contains third and fourth gasification chambers24 and 26, respectively. The chambers 16, 18, 20, 24, 26, and 22 aredivided by a plurality of generally vertical partitions 42, 44, 46, 48,and 50 respectively. Partition 42 may, in one non-limiting embodiment,extend from the top and bottom of the interior of vessel 12 and have anaperture 52 in the middle thereof to permit the fluid to flow into firstgasification chamber 18. Partitions 44, 46, 48, and 50 extend from theinterior top of vessel 12 downward, and are spaced away from theinterior bottom of vessel 12 to allow fluid communication between theadjacent chambers therebeneath. The flow of liquid 14 follows liquidtransport path 36 through the vessel 12, although within each chamber,some back flow 40 of liquid 14 into the impeller or rotor 38 will occurduring agitation and mixing.

Each gasification chamber 18, 20, 24 and 26 may be, but is not requiredto be, essentially identical in design. Only gasification chamber 20 isshown in detail, and it may be assumed for the purposes of thisnon-limiting explanation that the other gasification chambers are thesame or very similar. Each gasification chamber 18, 20, 24, and 26 willhave a vapor space 54 above the liquid 14 level 15, but the vapor spacesof the adjacent chambers are not in communication with one another. Mostpreferably, there is an absence of communication between the vapor spaceof any gasification chamber with the vapor space of any othergasification chamber. The lengths of partitions 42, 44, 46, 48, and 50are calculated to minimize the effect of pressure differential due todifference in flow rates under each respective partition.

Inlet chamber 16 has an inlet 30 to introduce the flow of liquid 14 tothe inlet chamber 16. Each gasification chamber 18, 20, 24 and 26 has atleast one mechanism 32 for ingesting and mixing gas into the liquid ofeach respective gasification chamber 18, 20, 24, and 26 for creating aturbulent area where the second gas 66 displaces the first gas to anupper portion or vapor space 54 of the vessel 12 for each respectivechamber 18, 20, 24, and 26. Gas ingesting and mixing mechanisms 32, inone non-limiting embodiment, may be submerged rotor mechanisms, and arepreferably the devices of U.S. Pat. No. 3,993,563, incorporated byreference herein. Mechanisms 32 may also be depurators. Mechanisms 32,such as described in U.S. Pat. No. 3,993,563, may each include one ormore gas standpipe ports 55 to transfer gas into the rotor assembly ofmechanism 32 from the vapor space 54 in the upper portion of vessel 12.Generally, mechanisms 32 create a vortex that draws gas from vapor space54 into the liquid. It is not the intent of the apparatus or method torecirculate gas from the vapor space when removing, replacing ordisplacing the first dissolved gas with a second ingested gas. Thesecond gas 66 will be introduced via an external gas connection or feed58 from second gas feed line 59 which will be attached to a sourceexternal to vessel 12.

The gas ingesting and mixing mechanisms 32 obtain their source of secondgas 66 from gas feed or inlet 58 off second gas feed line 59 in eachgasification chamber 18, 20, 24, and 26. The second gas 66 may be, inone non-limiting embodiment, natural gas, which is typically found alongwith the hydro-carbons in the subterranean formation 104, or may be adifferent gas. Each gas inlet 58 may be located within the standpipediameter of each gasification chamber 18, 20, 24, and 26 in onenon-limiting embodiment herein. Vertical draft tube 56 of generallycylindrical configuration may be present between impeller 38 and vaporspace 54. Communication between gas feed 58 and the gas ingesting andmixing mechanisms 32 is by means of conduits not shown in the Figure.Second gas 66 may be, but is not necessarily, injected into the vaporspace 54 in each chamber 18, 20, 24 and 26. Instead, the first gas 74(e.g. CO₂) displaced from the fluid 14 collects in the vapor spaces 54and is removed from vessel 12 by tank exhaust 60 through vents 28, atleast one of which is located in each chamber 18, 20, 24, and 26. Insome cases it is permissible for a portion of second gas 66 that passesthrough the liquid in each chamber to be channeled through tank exhaust60, although in the embodiment where second gas 66 is natural gas, itshould, of course, not be vented to the atmosphere. It may be desirableor necessary for the vents 28 from the vapor space 54 in eachgasification chamber to be equipped with a one-way gas valve to preventbackflow of the displaced first gas 74. That is, it is not a requirementof the apparatus or method that all of the second gas 66 introduced intovessel 12 be carried out in fluid 14 as it exits through outlet 34,although this is the more typical expectation.

The second gas, e.g. natural gas, is induced into the liquid, e.g.water, to have the first gas 74 removed by the mechanisms 32. Thisprocess also provides a means of controlling the partial pressureparameters, and allows the second gas 66 to displace the first gas 74,e.g. CO₂, thus scavenging CO₂ from the water 14. The first gas 74 isphysically not chemically displaced from the fluid 14 by the second gas66 in this process. Henry's Law of partial pressures requires that thefirst gas 74 be displaced as the second gas 66 is introduced. With eachsucceeding chamber, more of the first gas 74 is replaced at each point.The number of stages or chambers is not critical, but should besufficient in number to reduce the concentration of the first gas 74 inthe fluid to the desired level. It is expected that several gasificationchambers would be necessary to remove sufficient amounts of the firstgas 74 in most cases. It should be apparent that the method herein is acontinuous process. It is desirable to predict and control the amount ofsecond gas 66 ingestion based on rotor submergence of 32 and speed ofrotor or impeller 38 to achieve the desired removal level for the firstgas 74, and the rate at which the second gas 66 is ingested.

Gas ingesting and mixing mechanisms 32 may also include water drafttubes (not shown) to transfer water 14 into the rotor assemblies ofmechanisms 32 exclusively from the bottom of the vessel 12. Inclusion ofthe water draft tube facilitates capacity variations within the samegeometry because all water 14 that enters the rotor assembly is directedto the rotor suction from the bottom of vessel 12, reducing fluidby-pass and short circuiting of the fluid 14 around the turbulent areas.The treated effluent flows out of vessel 12 via outlet 34 which may havea valve therein (not shown). Flow through the vessel 12 is maintainedvia pumps or innate system pressure (not shown).

Another part of mechanical flotation device 10 is an acid conduit 76 forintroducing acid 68 into at least the first gasification chamber 18, andlikely the other gasification chambers 20, 24 and 26, via acid feedtubes 78. The acid is to treat and remove or convert the alkalinespecies in the fluid 14 of which there is at least one in fluid 14. Inone non-limiting embodiment, the alkaline species is calcium carbonate,more accurately thought of as calcium bicarbonate, Ca(HCO₃)₂. In anothernon-restrictive version, the acid is sulfuric acid (H₂SO₄), although itmay be understood that other acids (e.g. hydrochloric or HCl) may beused in some embodiments. The reaction (I) in this non-limitingembodiment may be represented as:H₂SO₄+Ca(HCO₃)₂→CaSO₄(gypsum)+2H₂O+2CO₂↑  (I)The gypsum is soluble in the water and precipitates later in the limesoftening clarifier 116, the water product stays in the water 14becoming clarified, and the evolved carbon dioxide is removed from thewater 14 as previously described. The acid dosage to reduce alkalinityexpressed is based on stoichiometric. For instance, for each ppm ofH₂SO₄ added, there is 0.88 ppm of CO₂ produced.

In another non-restrictive, optional version herein, the vessel 12 isprovided with an alkali (basic material) feed tube 86 in at least thelast gasification chamber or cell for introducing alkali therein. Thealkali could also be alternatively or additionally added to theclarified water 70 downstream. As previously described, certaindownstream processes, for instance RO or nano-membrane processes mayperform better in a high pH environment. Additionally, feed water to thewet steam generator 119 will require a pH of 9 or higher. In anothernon-limiting embodiment of the invention, the vessel 12 may be providedwith at least two pH probes 88 and 90, one each in the first and last(fourth, in this non-limiting example) gasification chamber 18 and 26,respectively, as schematically illustrated in FIG. 2. These pH probes 88and 90 are adapted to measure and/or indicate and transmit the pH valuesuch that the chemical feed rates of acid introduction from the acidfeed tubes 78 and/or the rate of alkali introduction from alkali feedtube 86 may be adjusted to meet the stated goals herein. Optionally, allgasification chambers may be provided with a pH probe.

The alkali (basic material) may typically be sodium hydroxide (NaOH) asthe most common choice, although other suitable alkalis include, but arenot necessarily limit to potassium hydroxide (KOH), soda (sodiumcarbonate, Na₂CO₃), or any compound containing OH⁻ ions. As anon-limiting example, NaOH will be used in a typical example. If thewater contains excessive alkalinity, the added NaOH is consumed byreacting with alkalinity as indicated in the following equation:Na(HCO₃)+NaOH→Na₂CO₃+H₂O  (II)It should be noted that there is no pH change because the alkalinityacts as a buffer. If acid is used to reduce the alkalinity, then thereaction is as in equation (I). Note that this water is now neutral inpH. Any small amount of NaOH added will raise the pH significantly.

Some very important goals are accomplished by the apparatus and methodsherein: (a) the addition of acid 68 converts alkalinity to CO₂ and waterby injecting and mixing acid in the each chamber (primarily the firstchamber 18, in one non-limiting embodiment), (b) the introduction ofscrubbing gas 66 (e.g. natural gas) to strip CO₂ from the productionwater 14, (c) the raising of pH due to the removal of CO₂ from theproduced water, and (d) the raising of pH due to the optional additionof alkali such as NaOH or KOH to the clarified water to meet downstreamneeds. The removal of CO₂ will reduce the lime requirement for limesoftening downstream in unit 116.

A fifth goal of (e) the removal of oil 72 from the produced water 14 isaccomplished by skimming the oil or other suspended oily matter orhydrocarbon from the surface 15 of liquid 14, such as by using channelsor troughs 80 in each chamber 18, 20, 24 and 26. The oily matter ischanneled through pipes 82 to collection conduit 84 to yield skimmedhydrocarbons 72. Skimmed hydrocarbons 72 may be processed and combinedwith hydrocarbon portion 114 for further handling and refining.

There may also be present in vessel 12 a liquid level controller 62 ofany suitable kind, to regulate the rate at which fluid 14 enters vessel12. The apparatus 10 may also have a control mechanism, such as aprogrammable logic controller (PLC) (not shown) for controlling theliquid level 15 in the gasification chambers 18, 20, 24, 26 by obtaininglevel information from level transmitters (not shown) and regulating theliquid flow through level control valves (LCVs, not shown) which may bein fluid communication with the liquid in each chamber, and flow controldevices to regulate flow of gas and acid to and from the vessel. Theexact natures of the control devices and overall control system are notcritical and may be conventional in the art; however, theirimplementation in the scavenging and treatment apparatus 10 is expectedto be inventive.

In another non-restrictive embodiment, the gas scavenging and liquidtreatment apparatus 10 has a dual-cell design, that is, only twogasification cells, 18 and 20, but more may be used as seen in FIG. 2.An optional chemical scavenging feed unit (not shown), which is astandard feed unit for dispensing a metered amount of a first gasscavenging chemical, into fluid 14, to additionally treat the fluid forachieving optimum separation of the first gas 74 from the water 14 maybe provided. This optional chemical treating may occur in outlet chamber22, but may occur in other chambers instead or in addition thereto.However, it may be appreciated that such an additional chemicalscavenger treatment may not be necessary. Other optional additives mayinclude, but are not necessarily limited to polymers in lowconcentrations for coalescing oil droplets, e.g. ionic polymers such ascation polymers.

Although not shown, valves may be provided for blowdown of sludge thatcollects in the bottom of vessel 12. A drain 64 for cleaning out vessel12 may also be provided. Also not shown are optional gauges to monitorthe pressure of the effluent and the flow of gas.

In the method herein, a continuous flow of liquid 14 having a first gas74 (e.g. CO₂) mixed or dissolved therewith is introduced into inletchamber 16 through inlet 30. Fluid 14 flows past partition 42 into thegasification chambers 18, 20, 24, and 26 sequentially via liquidtransport path 36. In each chamber a flow of second gas 66 (e.g. naturalgas) is introduced into the water 14 by gas ingesting and mixingmechanisms 32, creating a turbulent area in the entirety of chambers 18,20, 24, and 26, and allowing the second gas 66 to physically displacethe first gas 74. The first gas 74 is forced out of the liquid 14 asbubbles to the upper portion of vessel 12 where it collects in therespective vapor space 54 of each chamber. First gas 74 is collectedthrough vents 28 and removed through tank exhaust 60.

Acid 68 is introduced into the fluid 14 of chamber 18 to react with thealkaline species (e.g. Ca(HCO₃)₂) such as according to reaction (I) inone non-limiting embodiment. The water product stays in fluid 14 and thecarbon dioxide by-product is removed as described with respect to firstgas 74. At least some oily matter suspended on the surface 15 of water14 is collected by channel 80.

Fluid 14, progressively more free of first gas 74, alkaline species andoily matter, next underflows each partition 44, 46, 48, and 50 in turnflows through liquid outlet 34. It will be appreciated that it is notpossible to predict with accuracy how much of the first gas 74 may beremoved from the liquid 14 since such removal depends upon a number ofcomplex, interrelated factors including, but not limited to, the natureof the gases, the nature of the liquid, the concentration of the firstgas 74 in the liquid, the ability of the liquid 14 to absorb the secondgas 66, the temperature of the liquid 14, the pressures within thevessel 12, and the like. Further, depending upon downstreamrequirements, additional alkali may be optionally added via alkali feedtube 86. As previously mentioned, the feed rates of acid introducedthrough acid feed tubes 78 and/or the alkali feed rate introducedthrough alkali feed tube 86 may be controlled at least partly frominformation measured and related by pH probes 88 and 90. For instance,this information may go to PLC which in turn controls valves (not shown)regulating the introduction of acid and/or alkali to meet the goalsherein previously discussed.

The rate at which clarified liquid 70 is removed from vessel 12 may beregulated by a valve or valves (not shown) in response to softwareprogram commands or other control mechanism.

To summarize, advantages of the apparatus and methods described hereininclude, but are not necessarily limited to, decreased number oftreatment stages by simultaneous reduction in suspended matter andalkalinity of the feed water for steam flood or other similar watertreatment facilities, resulting in simplification of operation andreduced capital costs, particularly as compared with a process wherethese functions are performed separately. In other words, threetreatment stages are combined into one. These advantages are achievedthrough a first gas scavenging machine (e.g. depurator) using physicalmethods to displace a first undesired gas with a second gas. Alkalinespecies are treated with acid. The removal of originally present CO₂ andCO₂ byproduct raises the pH of the water to reduce the lime requirementin a downstream lime softener. If the pH of the water needs to be raisedfurther, alkali such as NaOH may be optionally added near or at the laststage of the apparatus. Oily matter and the like are successivelyskimmed from each chamber for essentially complete removal. In mostexpected methods of using the apparatus, it is anticipated that theeffluent only contain small quantities of the second gas. Alternatively,it may be that the liquid contains appreciable amounts of the secondgas, and this is acceptable.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in providing a device and apparatus for removing or strippingan undesired gas from a liquid, simultaneously removing or reacting atleast one alkaline species therein, and optionally removing oilycontaminants at the same time. However, it will be evident that variousmodifications and changes can be made thereto without departing from thebroader spirit or scope of the invention as set forth in the appendedclaims. Accordingly, the specification is to be regarded in anillustrative rather than a restrictive sense. For example, the distancesbetween the partitions and the volumes of the various chambers may bechanged or optimized from that illustrated and described, and eventhough they were not specifically identified or tried in a particularapparatus, would be anticipated to be within the scope of thisinvention. Similarly, gas ingestion and mixing mechanisms, and leveltransmitting and control devices different from those illustrated anddescribed herein would be expected to find utility and be encompassed bythe appended claims. Different first and second gases, differentalkaline species and acids, different alkalis and different oily matterother than those described herein may nevertheless be treated andhandled in other non-restrictive embodiments of the invention.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed.

The words “comprising” and “comprises” as used throughout the claims isto interpreted “including but not limited to”.

What is claimed is:
 1. A method for simultaneously removing a first gasand at least one alkaline species from water, the method comprising: a)providing a vessel comprising an inlet and an outlet and a plurality ofpartitions sequentially dividing the vessel into at least a firstgasification chamber and a second gasification chamber, each adjacentchamber fluidly communicating with one another, each chamber having avapor space, in the absence of communication between the vapor spaces ofadjacent chambers; b) introducing a flow of water comprising a first gasand the alkaline species into the first gasification chamber through theinlet; c) introducing an acid into at least the first gasificationchamber; d) introducing a flow of a second gas into each of thegasification chambers creating a turbulent area, and displacing at leasta portion of the first gas from the water into the vapor space of therespective gasification chamber with the second gas, and reacting theacid with at least a portion of the alkaline species; e) removing thedisplaced first gas from the vapor space of each gasification chamber;and f) removing the clarified water from the vessel through an outlettherein.
 2. The method of claim 1 further comprising introducing an acidinto each gasification chamber.
 3. The method of claim 1 whereintroducing the flow of second gas into the gasification chambersincludes ingesting and mixing the second gas with the water.
 4. Themethod of claim 1 where the residence time for each gasification chamberis about one minute.
 5. The method of claim 1 where the first gas iscarbon dioxide and the second gas is natural gas.
 6. The method of claim1 where the alkaline species reacts with the acid to form carbondioxide.
 7. The method of claim 1 where the pH of the removed water isincreased over that of the water introduced into the vessel.
 8. Themethod of claim 1 where the water further comprises oil and the methodfurther comprises skimming the oil from a water surface into a channelin each gasification chamber.
 9. The method of claim 7 furthercomprising simultaneously reducing suspended matter, alkalinity and pHadjustment of the water, resulting in simplification of operation andreduced operating and capital costs as compared with a process wherereducing suspended matter, alkalinity and pH adjustment of the water areperformed separately.
 10. The method of claim 1 where the clarifiedwater is further transported to a lime softener and the lime requirementof the clarified water is reduced compared to the lime requirement ofthe water entering the vessel.
 11. The method of claim 1 furthercomprising introducing a basic material into at least a lastgasification chamber.
 12. A method for simultaneously removing a firstgas, oil and at least one alkaline species from water, the methodcomprising: a) providing a vessel comprising an inlet and an outlet anda plurality of partitions sequentially dividing the vessel into at leasta first gasification chamber and a second gasification chamber, eachadjacent chamber fluidly communicating with one another, each chamberhaving a vapor space, in the absence of communication between the vaporspaces of adjacent chambers; b) introducing a flow of water comprising afirst gas and the alkaline species into the first gasification chamberthrough the inlet; c) introducing an acid into at least the firstgasification chamber; d) introducing a flow of a second gas into each ofthe gasification chambers creating a turbulent area, and displacing atleast a portion of the first gas from the water into the vapor space ofthe respective gasification chamber with the second gas, and reactingthe acid with at least a portion of the alkaline species, where saidintroducing includes ingesting and mixing the second gas with the water;e) removing the displaced first gas from the vapor space of eachgasification chamber; f) removing the clarified water from the vesselthrough an outlet therein; and g) skimming the oil from a water surfaceinto a channel in each gasification chamber.
 13. The method of claim 12further comprising introducing an acid into each gasification chamber.14. The method of claim 12 where the residence time for eachgasification chamber is about one minute.
 15. The method of claim 12where the first gas is carbon dioxide and the second gas is natural gas.16. The method of claim 12 where the alkaline species reacts with theacid to form carbon dioxide.
 17. The method of claim 12 furthercomprising simultaneously reducing suspended matter, alkalinity and pHadjustment of the water, resulting in simplification of operation andreduced operating and capital costs as compared with a process wherereducing suspended matter, alkalinity and pH adjustment of the water areperformed separately.
 18. The method of claim 12 where the pH of theremoved water is increased over that of the water introduced into thevessel.
 19. The method of claim 12 where the clarified water is furthertransported to a lime softener and the lime requirement of the clarifiedwater is reduced compared to the lime requirement of the water enteringthe vessel.
 20. The method of claim 12 further comprising introducing abasic material into at least a last gasification chamber.